Key Evolutionary Terms
Adaptive Traits: Are any characteristic that aids survival and success in the environment
Reproductive Fitness: Liklihood of passing genes on to offsprin
Natural Selection: Adaptive traits are chosen by the environment and aid survival, those who do not have these traits will die so maladaptive genes will not be passed on
Competition: Occurs when two animals of the same sex are attempting to mate with the same partner
Lorenz (1966) believed that in animals there are 3 main reasons for them to become aggressive;
1. Mating as the fittest male is chosen
2. The protection of young
3. In order to divide territories
We have evolved to be aggressive in order to survive.
Evolutionary Explanations for Aggression
There are 2 reasons that have been widely studied that can explain aggression in evolutionary terms:
- a state of fear caused by a real or imagined threat to their status as an exclusive sexual partner, more common in males
- the act of being unfaithful: the cause of jealousy (when it is real or imagined)
Research has shown that males are more affected by sexual jealousy. This is because:
- They need women sexually, more than they need men (males cannot get pregnant, they need a woman to carry their child)
- If their partner is unfaithful, they cannot pass on their genes and have to use their resources to raise another man's offspring
Daly and Wilson argue that mate retention (trying to keep your mate) is important to animals; especially males, as this increases reproductive fitness because without a mate to bear his children, a male's genes will not be passed on. Animals have developed a range of techniques to ensure mates do not commit adultery:
- Violence and the threatening of
- Direct guarding: stopping other males having access to the female or looking through personal belongings
- negative inducements (shout at your partner),
- emotional manipulation
Female mate retention tactics:
- verbal possession signals,
- threats of punishing infidelity
Buss believed that infedelity triggers an emotional response which leads to violence. An example of this is cuckoldry. Cuckoldry is when a female deceives her partner into believing an offspring is his own, and he uses his resources into raising it, although it was conceived by another male.
The consequences for cuckolded males are:
- They use their resources (food, time, territory)
- They protect an offspring that isn't theirs
- they invest time and energy into raising the offspring
Evaluation of Jealousy and Infidelity
Buss and Shackelford studied mate retention tactics in 107 couples. Males were more likely to report debasement (e.g. giving in to her every wish) and threatening physical violence (e.g. beating up another man) than women. Women were more likely to report verbal possession signals (e.g. telling other women he's taken) and threats of punishing infedelity (e.g. leaving a male partner if he was ever unfaithful). This supports the evolutionary theory because males are more aggressive in response to jealousy because they try to avoid cuckoldry.
Men married to younger women devoted more effort to mate retention tactics, including commitment manipulation (eg professing love), violence against rival men and threats against the female partner. This supports the theory because younger women will attract more competition, increasing the risk of cuckoldry, therefore the males will be more aggressive.
Involved 461 American males, with a mean age of 24 years, in relationships for a mean of 37 months.
The men completed a Mate Retention Inventory concerning their use of 104 different mate retention strategies. A violence score was also established, based on how often they were towards their partner.
Results showed that men who used negative inducements (eg shouting at their partner for looking at another man), direct guarding their partner in social situations (eg monopolize her), and used emotional manipulation (eg making her feel guilty or threatening to kill self if she left) were more likely to use violence (positively correlated). This supports the theory because as expected, jealousy leads to increased aggression
However, the men could be lying - social desirability bias. Therefore; may not accurately reflect levels of violence in relationship, reducing the study’s support for the theory. Quite a big sample compared to other studies.
Involved 560 American females, with a mean age of 21 years, in relationships for a mean of 29 months. The women answered questions on their partner’s use of mate retention strategies and any violence that had been used towards them.
The findings confirmed the validity of study 1. Male partners who used negative inducements, direct guarding, and emotional manipulation were more likely to use violence.This supports the idea that high rates of jealousy increase aggression.
However, you can't establish cause and effect, reducing the support for the theory.
Use of mate retention tactics
The claim that sexual jealousy is a major cause of violence against women is supported by studies of battered women, where victims frequently cite extreme sexual jealousy on the part of male partners as the cause of violence against them (Dobash and Dobash) This supports evolutionary explanation of aggression because it suggests aggression has evolved in response to jealousy to prevent infidelity.
The use of direct guarding as a mate-retention tactic is also evident in a study by Wilson et al, who found that among women who reported the use of these tactics by their male partners (e.g. not allowing her to talk to other men) 72% had required medical attention following an assault by their male partner.
Research on sexual coercion – partner ****
Research tends to support the idea that sexual coercion of females by their male partners is an adaptive response to the threat of infidelity. Camilleri found that the risk of a partner’s infidelity predicted the likelihood of sexual coercion in men but not women. This is important for an adaptive explanation, as it is men who are at risk of being cuckolded, not women.
Goetz and Shackelford also found that men who had sexually coerced their partners were more likely to report that they thought their partners were being unfaithful. Women who reported that their partners had sexually coerced them were more likely to admit to having been unfaithful.
Practical applications of research
An important implication of research in this area is that mate-retention tactics may be seen as early indicators of potential violence against a female partner. The use of mate-retention tactics can alert friends and family members to the danger signs that might lead to future violence in relationships. Relationship counselling may then be used before the situation escalated into the type of violence reported in the Dobash and Dobash study described above.
- The theory is too determinstic and ignores free will; it assumes a man will be violent to their partner when jealous
- moreover, it implies that aggression and domestic violence is not the man's fault because his actions are determined by his genes
- Reductionist – complicated behaviour that is explained by a simple theory
- There are equally plausible alternative explanations for male violence towards women (e.g. learning theory and psychodynamic theory)
- it ignores other factors such as the environment (focuses on nature)
- could be explained by social learning theory; if a male watched his father do abuse his mother, he might do the same in the future
The Evolution of Murder
Someone ending someone else’s life in the same species with intent.
The male lion murder cubs once he has taken over the pride as the new alpha male to avoid cuckoldry and them challenging him in the future.
Buss and Duntley (2006) proposed that humans have adapted four main characteristics which activate the behaviour of murder;
- Degree of genetic relatedness; not beneficial for you to kill your own children
- The status of victim and killer
- The sex of killer and victim
- The size and strength of the killers and victim’s families or social groups
Perhaps there are occasions where murder is a successful strategy in improving reproductive fitness.
Buss and Duntley continued
They believed that in most circumstances, the high cost of committing murder would be outweighed by other competing strategies. However, as this behaviour still exists there must be occasions where murder is an adaptive response:
- Genetic relatedness: Parents might kill the weakest child to reserve resources for their stronger children and increases the chance of them passing on genes.
- Status: To become the leader (alpha male) so that you can have more resources and higher reproductive fitness because you have access to the women of the group
- Sex: It is more adaptive for males to kill other males because then they have access to the women and have higher reproductive fitness. Moreover, they avoid cuckoldry
- Family/Group size: To protect your territory and resources, which will sustain your life and then increase your reproductive fitness because you are alive.
Buss and Duntley also claim that for our ancestors murder could solve adaptive problems such as:
- Preventing harm – in self-defence or to defend your children
- Reputation management – to avoid being seen as a pushover (being easily exploited, otherwise people would take advantage and take over and challenge you
- Protecting resources – you would kill to protect your resources to look better in the eyes of the pack and females, this improves your reproductive fitness. For women, you can protect your children by killing people trying to take their resources
Predisposing factors for murder - gender
Daly and Wilson (1988) proposed that although most murders are committed by men this behaviour is not restricted to men. Men and women both murder but for different reasons.
Men – Jealousy, to avoid cuckoldry, status, resources, territory
Women – protection of themselves or of their young, protect their resources to sustain themselves and their children
Percentages of murder:
Male offender/male victim 65.3%
Male offender/female victim 22.7%
Female offender/male victim 9.6%
Female offender/female victim 3.4%
The high murder rates support the idea that males have more reason to murder from a evolutionary perspective.
Wilson and Daly also identified factors they believed affected the chances of murder for example males are most likely to commit a murder in their 20’s when they are at their peak in reproductive competition. The reasons why are:
Sexual jealousy – love triangles (Daly and Wilson, 1988)
This appears to be an important cause of same-sex aggression and murder. Because of the association between infidelity and cuckoldry, men are predominantly both the perpetrators and also the victims. Daly and Wilson summarized data from eight studies of same-sex killings that involved ‘love triangles’ they found that 92% of these murders involved males killing males and only 8% involved females killing another female.
This supports the theory because we see more male-male violence, as males are the only gender at the risk of cuckoldry.
Lack of resources – unemployed murderers (Wilson and Daly, 1985)
Research on sexual selection in humans has shown that females are attracted to males who possess resources. Wilson and Daly suggest that a lack of resources increases male-male competition and the risk of murder. They cite murder statistics in Detroit, which showed that 43% of the male victims and 41% of the male perpetrators were unemployed, although the overall unemployment rate for adult males in Detroit at that time was just 11%.
This supports the evolutionary theory, as the men are trying to get resources and kill competition to improve their reproductive fitness.However, the percentage of unemployed victims was higher than the perpetrators. If this was the case, surely the percentage of unemployed perpetrators would be higher? There would be no need to kill unemployed men, as they are less competetion. Yet, the percentage is still high.
Threats to male status – income inequality and murder
The biggest single factor related to murder is maleness, the second is youth. In addition to sexual jealousy and lack of resources, threats appear to be an important determinant of murder among young men. Daly and Wilson argue that females are attracted to males who are dominant over other males and therefore, men are shaped by evolution to seek status.
When there is intense competition for scarce resources this status is more likely to be threatened than when these resources are in generous supply. Daly and Wilson cite a strong correlation between degree of income inequality and murder rates – countries with more income inequality tend to have higher murder rates.
According to the evolutionary perspective, loss of male status would have been catastrophic for the survival and reproduction of our ancestors and mechanisms to prevent loss of status still operate today when triggered by threatening events
This supports the evolutionary theory because higher income inequality induces men to commit murder to have a higher status.
- Murder as an adaptation is supported by comparative studies of other species. As we have seen male lions kill the offspring of rival males (Ghiglieri, 1999). This has also been observed in gorillas (Fossey, 1984) and chimpanzees (Wrengham and Peterson, 1996)
- Evolutionary theory is too reductionist- An alternative explanation is the Evolved Goal Hypothesis by Hardy (1999). He believed humans have evolved motivations for specific goals e.g. to strive for status and acquire a mate for reproductive success. These goals were reached by using evolved problem solving behaviour that best suited the situation, these were decided upon by conducting a cost benefit analysis of the situation and in some cases murder could be the most effective action.
- We can not compare the behaviours on animals and humans as we are fundamentally different in many areas e.g. logic, language etc (Lehrman, 1953)
- Gender bias – females do sometimes act violently against their male partners. Archer (2000) found in family conflict studies that there are equal rates of assault for men and women.
- It does not explain why people act so differently in the same situation.
- Buss and Shackelford give the example that when a woman is unfaithful, some males will behave aggressively whilst others will just leave. The evolutionary approach cannot explain these differences.
- It does not explain cultural differences.
- Buss and Shackelford demonstrates this by comparing the Yanomamo tribe (a violent group that encourage violence) with the !kung San tribe (a placid tribe with almost non-existent violence as aggression is frowned upon
- it ignores violence in gay relationships, they cannot be cuckolded